Opportunistic screening for osteoporosis using thoraco-abdomino-pelvic CT-scan assessing the vertebral density in rheumatoid arthritis patients.

INTRODUCTION: Screening for osteoporosis is crucial in rheumatoid arthritis (RA) patients. The aim of this study was to assess the value of thoraco-abdomino-pelvic CT-derived bone mineral density (BMD) results in L1, compared to dual energy X-ray absorptiometry (DXA) results for osteoporosis screening in rheumatoid arthritis patients.
METHODS: Consecutive RA patients who underwent a CT-scan and DXA within a 2-year period were retrospectively included. The CT sagittal images were then evaluated for vertebral fractures from T4 to L5 using the Genant classification. The CT-attenuation values (in Hounsfield units (HU)) of trabecular bone in L1 were measured on axial images and compared to the DXA results.
RESULTS: This study included 105 patients (mean age 61.1 years (± 9.5), 78.1% women). There were 28 patients (26.7%) with DXA-defined osteoporosis and 32 (30%) with osteoporotic fractures (vertebral and/or non-vertebral). The CT assessment indicated that the mean (SD) vertebral L1 attenuation was 142.2 HU (± 18.5). The diagnostic performance for the vertebral CT-attenuation measurement was acceptable: the AUC was 0.67 for predicting osteoporotic fractures and of 0.69 for predicting vertebral fractures. Among patients with osteoporotic fractures, there were 23 (74%) patients categorized as osteoporotic with a L1 CT-attenuation of 135 HU or less, whereas there were only 13 patients (42%) identified by DXA.
CONCLUSION: CT offers a combined opportunistic screening for osteoporosis by assessing both vertebral fractures and bone density on routine CT-scans. This approach may be particularly interesting for RA patients with a high osteoporosis risk.